Needle wire



Patented May 11, 1937 NEEDLE Leslie D. Hawkridge, Newton Center, Mass, as-

signor to Crucible Steel Company of America, New York, N. Y., a corporation of New Jersey No Drawing. Applfcation May 11, 1935,

, Serial No. 20,990

8 Claims.

This invention relates to the swaging of steel wire, especially in the manufacture of needles. Needles are ordinarily made by cold swaging steel wire. The manufacture of needles in this manner has presented various difficulties of a serious nature due, for instance, to operations -necessary in processing, and to the properties necessary in the wire and needles. Thus, careful and accurate control of the steel analysis has been necessary, while painstaking care has been required in processing. Moreover, in th practice up to the time of this invention the life of the swaging dies used for making needles has been relatively short.

More in detail, needles may be classed generally into three types made from wire of different specifications. These are (l) sewing machine needle wire, containing from about 1.1 to 1.3 per cent of carbon, (2) spring beard needle wire, usually containing about 0.8 to 0.95 per cent of carbon, and (3) latch and latch needle wire, the common specification of which calls for about 0.6 to 0.85 per cent of carbon. The specifications for these three types of wire have been quite rigid as to sulfur content, providing for a' maximum of 0.02 per cent of sulfur. This has'been due to the prevailing belief heretofore that sulfur in excess of the amount specified exerts a deleterious action. With the limitations on the carbon content, and with the rigid specification for sulfur content, it will be realized that extreme care has been required in the manufacture of stock for such wires.

Referring to the. difiiculties which have at tended processing, the production of needle wire involves a long series of. drawing and annealing operations, and great care has been necessary in conducting the latter to avoid the formation of graphitic carbon in the wire. The avoidance of graphitizing is necessary because even traces of graphiticcarbon render the wire useless for the production of needles. Consequently, if graphitic carbon is precipitated during annealing the wire must be scrapped. 45 To overcome or counteract the tendency to graphitize in high carbon steels of the types used for needle wire it has been proposed to add elements, such as chromium and vanadium, intended to form carbides, or to stabilize carbides. and also to render the needles stronger and springier. The use of such additional alloying elements, however, has not met with any particular success, and has, in fact, been largely abandoned because even in the small amounts in 'which they are used, such alloying elements so harden the wire as substantially to increase the swaging difficulties. The importance of this factor is readily understandable from the fact that with plain carbon needle wires of the foregoing types the swaging dies ordinarily have a relatively short life. For instance, in making sewing machine needles the initial swaging operation involves tapering the working end of the stock to a thickness about one-half the initial diameter of the wire. In such an operation the needle blank for about three-fourths of its length undergoes a reduction in area of approximately 70 per cent of the original cross sectional area of the wire. It is well known in the art that swaging die failure in this operation is a serious problem, and in fact the dies used in this step commonly produce a maximum of about 3500 needles. Such low die life adds materially to the cost of the needles. If the wires are hardened by the use of alloying elements it ordinarily follows that the die life would be decreased.

It is among the objects of this invention to provide needle wire stock which is of improved swagability and provides substantially increased die life, overcomes, or minimizes, the foregoing and other disadvantages heretofore present in the art, which represses or eliminates processing difliculties, such as those attendant upon annealing, and which renders the use of special alloying elements commercially feasible. Other objects will appear to those skilled in the art from the following description.

The invention resides in my discovery that, contrary to the belief in the art, sulfuris beneficial in needle wire, and that by its use the difficulties heretofore encountered in the manfacture of needle wire and needles are suppressed, and that major benefits flow from such modification of the composition of needle wire. The invention applies generally to needle wire stock, but it may be stated by way of example to apply to steel needle wire containing about 0.6 to 1.3 per cent of carbon, which includes the ranges of the three types discussed hereinabove, these being well known and therefore forming good illustrative examples.

A surprising feature of the invention is that extremely small amounts of sulfur suflice to produce the substantial benefits which flow from 1e invention. Thus, the steels used in this invention contain more than about 0.025 per cent of sulfur, which usually suflices with the plain carbon steels, and generally not more than about 0.08 per cent of sulfur is necessary in such steels 55 for the purposes of the invention, although higher sulfur contents may be used, if desired, for special purposes.

Molybdenum may be, and in some embodiments is, added also to the steels, especially in the higher ranges of sulfur, to neutralize the tendency of sulfur to render the wire hot short. Extremely small amounts of this element also suflice for the purposes of the invention, for example, as little as 0.04 per cent. More molybdenum may, of course, be added, e. g., up to 0.5 or 1 per cent, depending upon the sulfur content of the steel, andupon the production of desired mechanical properties;

The remainder of the steels maybe made up of iron together with impurities and elements added for purposes apart from those of the invention, and in amounts not adversely affecting the properties conferred by the sulfur, or by sulfur and molybdenum. Since the essential elements are sulfur, or sulfur and molybdenum,

the remainder of the steels is referred to, for brevity, as being substantially iron.

As an example of the invention, reference may be made to a sewing machine needle wire embodied in the invention and used commercially, containing about 1.2 per cent of carbon, 0.1 per cent of chromium, 0.29 per cent of manganese, 0.1 per cent of molybdenum, 0.09 per cent of nickel, 0.014 per cent of phosphorus, 0.24 per cent of silicon, and 0.04 per cent of sulfur. The contents of carbon; manganese, phosphorus and silicon are those normal to' a steel of this type, while the chromium and nickel in this analysis are incidental, arising from the materials used rather than being added intentionally. The sulfur content, however, is double-the maximal content of prior specifications, and the molybdenum content is in accordance with the present invention. Using such a steel without the high sulfur, or the sulfur. and molybdenum, the difficulties described hereinabove would be encountered, and at best the swaging dies would produce about 3,500 needles when applied to the initial swaging step as referred to hereinabove. The swaging characteristics of the foregoing steel containing sulfur and molybdenum in accordance with the invention are so markedly improved, however, as determined by actual commercial practice, that in the same initial swaging operation as many as 36,000 needles may be made per die, thereby not only decreasing the swaging difiiculties, but also greatly reducing die costs. On the average the steel wire provided by this invention produces about 20,000 to 25,000 needles per die.

Other analyses illustrative of steels actually made in accordance with the invention, and exemplifying its application to other types of wire, in which the chromium and nickel contents again are incidental, not intentional, are as follows:

Bteel A Steel B Carbon 0.87 0.76 Chromium 0.06 0.07 Manganese. 0. 32 0. 30 Molybdenum. 0.10 0.09 Nickel"--. 0.09 0.09 Phosphorus 0. 012 0. 012 Silicon. 0. l8 0. 1e Sulfur (104 0.05

Sulfur and molybdenum have been embodied heretofore in steels for the purpose of producing free machining properties. customarily, however, much larger amounts of these two elements have been necessary for that purpose than are required in the practice of this invention. For instance, sulfur in an amount of about 0.15 per cent is usually the minimum productive of free machining properties in the diillcultly machinable steels, and much more is necessary in the highly alloyed steels, for example, up to about 0.5 per cent, or more, and the requisite molybdenum content is correspondingly high. While these two elements have been productive of free machining properties, their known effect on other properties of steels has been such that metallurgists have considered their use disadvantageous from certain standpoints. For example, it is-known that free-machining steels containing sulfur and molybdenum contain, as a result of those elements, non-metallic impurities in the form of sulfide stringers. Such nonmetallic impurities introduce a certain weakness factor, and it is known that those steels can not, as a result, be cold headed or similarly cold formed as satisfactorily as similar steels which do not have the high content of sulfur and other elements, such as molybdenum.

The difficulties heretofore attendant upon the production of needles by die swaging, and the precautions necessary in the processing of the wire and during the swaging operations, have been such that in view of the foregoing adverse effect of sulfur and molybdenum on other steels the normal belief would have been that the difficulties actually would be increased. The contrary is true, however, as I have discovered.

In the steels used in the practice of this invention manganese, phosphorus, silicon and other elements may be those normally present in the steels, or normally attendant upon their manufacture. An important feature, however, is that by the use of sulfur, or sulfur and molybdenum, in accordance with the invention the swaging characteristics are so improved as to permit the use of alloying elements for desired purposes while avoiding the disadvantages heretofore attendant upon their use. Thus, the annealing and processing dimculties can be overcome by adding carbide-forming or stabilizing elements, such as chromium and/or vanadium, without, however, causing the swaging dificulties, referred to above, which have been encountered heretofore, and while retaining the improved swaging properties which as characteristic for this invention are superior to the swaging properties heretofore considered satisfactory in material not containing such stabilizing elements. Thus, such elements may be added in amounts effective to produce a desired result, usually not over about 1 per cent, the exact content depending, as metallurgists will understand, upon the properties desired and upon the contents of carbon, manganese and other elements present in the steel. For instance, 0.10 to 1 per cent of chromium, preferably less than about 0.5 per cent, may be added to the steels, or about 0.03 to 0.25 per cent of vanadium. Thereby there is obtained increased strength, springiness or stiffness, and hardness in the finished needles while still providing the improved swaging properties due to sulfur, and also decreasing the tendency toward graphitization during heat treatment. Ordinarily it will be desirable to increase the sulfur content somewhat when using such alloying elements, for example, to 0.12 per cent or even more. Other alloying elements may, of course, be similarly added for special purposes.

Most suitably the steels are prepared in an electric furnace, because thereby the composition control is obtained readily. Various modifications are possible in the practice of the invention, such as in the adaptation of the compositions to make needles of various types, or in the substitution wholly or in part, of sulfur by selenium, based on their close chemical relationship.

According to the provisions of the patent statutes, I have explained the principle of my invention and have described what I now consider to represent its best embodiment. However, I desire to have it understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.

I claim:

1. Wire stock for swaging into needles, the wire being formed of steel containing from about 0.6 to 1.3 per cent of carbon, and sulfur from about 0.025 per cent to 0.5 per cent, the remainder of the steel being substantially iron.

2. Wire stock for swaging into needles, the wire being formed of steel containing from about 0.6 to 1.3 per cent of carbon, sulfur from about 0.025 per cent to 0.5 per cent, and from about 0.05 per cent to about 1 per cent of molybdenum, the remainder of the steel being substantially iron,

3. Wire stock for swaging into needles, the wire being formed of steel containing from about 0.6 to 0.85 per cent of carbon, and sulfur about 0.04

per cent to about 0.12 per cent, the remainder of the steel being substantially iron.

4. Wire stock for swaging into needles, the wire being formed of steel containing from about 0.8 to 0.95 per cent of carbon, and sulfur about 0.04 per cent to about 0.12 per cent, the remainder of the steel being substantially iron.

5. Wire stock for swaging into needles, the wire being formed of steel containing from about 1.1 to 1.3 per cent of carbon, and sulfur about 0.04 per cent to about 0.12 per cent, the remainder of the. steel being substantially iron.

6. Wire stock for swaging into needles, the wire being formed of steel containing from about 0.6 to 1.3 per cent of carbon, and about 0.03 to 0.12 per cent of sulfur, the remainder of the steel being substantially iron.

7. Wire stock in accordance with claim 6, the 

